Cooktop gas safety valve hold open circuit with ceramic heater

ABSTRACT

A cooking gas safety apparatus is shown and described. The apparatus includes a cooking gas safety valve assembly that supplies cooking gas to one or more burners. The cooking gas safety assembly includes at least one coil that is energizable to hold the valve assembly in an open position when subjected to a current that exceeds a threshold value and a hold open circuit. The hold open circuit comprises the coil and a hot surface igniter that is in electrical communication with the coil. The valve assembly is actuated by manually opening the valve and energizing the igniter such that it receives a threshold current that corresponds to an autoignition temperature of the gas. At the threshold current, an electromagnet in the cooking gas safety valve assembly holds the valve open so that it remains open without user intervention. In the event of an igniter failure, the current flow to the coil ceases, causing the valve to shut and cease gas flow to the burner. In certain examples, hold open circuit allows the igniter to operate off of alternating current while the coil receives a time-varying, direct current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/047,088, filed on Jul. 1, 2020, the entirety of which is hereby incorporated by reference.

FIELD

This disclosure relates to gas safety valves with a hold open circuit that holds the valve open when a threshold current sufficient to heat a hot surface igniter to an autoignition temperature of the gas is reached.

BACKGROUND

Certain cooktops include safety features to ensure that cooking gas is only supplied to the burner once ignition is achieved. This ensures that uncombusted cooking gas is not supplied to the surrounding environment, which could lead to a fire or explosion.

In one known system, the user operates a gas control knob to manually actuate a gas valve and supply current to a spark igniter adjacent the burner. A thermocouple acts as a flame detector that generates a direct current when ignition is successful. At a certain threshold current, the current generates a magnetic field that holds the gas valve in the open position so the user can release the knob. The gas valve is configured to fail closed such that when no flame is present, the magnetic force drops below a characteristic force required to hold the gas valve open, causing it to close. The threshold current is sufficient to hold the valve in the open position, but not sufficient to open it. User intervention is required to open the valve by manually actuating it. The integrated gas valve and electromagnet is referred to as a “gas tap” in Europe.

Spark igniters are user-actuated igniters that create a brief electric discharge and a spark that ignites the gas. Thus, they cannot remain on to ensure continuous ignition. As a result, it is important to detect the presence of a flame, such as by using a thermocouple, to avoid supplying burners with uncombusted gas. However, there is a significant amount of lag time and/or dead time in generating the threshold current needed to hold the gas valve open following ignition because the thermocouple must be heated long enough to reach a temperature at which threshold current is generated. Typically, the user is required to continue to manually hold the gas valve open for five to ten seconds after ignition occurs due to the thermal response of the thermocouple.

Hot surface igniters are a possible alternative to spark igniters. Hot surface igniters are used to ignite combustion gases in a variety of appliances, including furnaces and clothing dryers. Some hot surface igniters, such as silicon carbide igniters, include a semi-conductive ceramic body with terminal ends across which a potential difference is applied. Current flowing through the ceramic body causes the body to heat up and increase in temperature, providing a source of ignition for the combustion gases. Other types of hot surface igniters, such as silicon nitride igniters, include a ceramic body with an embedded circuit across which a potential difference is applied. Current flowing in the embedded circuit causes the ceramic body to heat up and increase in temperature, providing a source of ignition for combustion gases.

Unlike spark igniters, hot surface igniters can be continuously energized to ignite cooking gas because it is the igniter surface temperature, and not a discrete burst of electric potential, that causes ignition. When used in conjunction with the gas safety valve assembly described above, the energization state of the hot surface igniter provides an indication that ignition has occurred (or will occur) which allows for the elimination of the thermocouple. However, some means is required to link the current used to energize the igniter to the current required to hold the gas valve open. Thus, a need has arisen for a cooking gas safety apparatus that addresses the foregoing issues.

SUMMARY

In accordance with a first aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly that is manually actuatable to an open position to allow the passage of the cooking gas. The valve assembly includes at least one coil that is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value. The apparatus further comprises a hold open circuit comprising a hot surface igniter and the coil, wherein the hot surface igniter is in electrical communication with the coil, and wherein no later than about eight seconds after the at least one coil is subjected to a current having the threshold current value, a surface of the hot surface igniter reaches at least an autoignition temperature of the cooking gas. In accordance with certain examples, the coil is a direct current coil. In accordance with other examples, the coil is an alternating current coil. In accordance with additional examples, the hold open circuit is operable in a full power mode and a reduced power mode. In preferred examples, no later than about six seconds and more preferably no longer than four seconds after the at least one coil is subjected to a current having the threshold current value, a surface of the hot surface igniter reaches at least an autoignition temperature of the cooking gas.

In accordance with a second aspect of the present disclosure, a method of supplying cooking gas to a cooktop burner is provided. The method comprises providing a valve assembly comprising a valve having an open position and a closed position, wherein when the valve is in the open position, the cooking gas passes through the valve. The valve assembly further comprises at least one coil that is energizable to hold the valve in the open position. The method further comprises manually actuating the valve to the open position, and supplying an alternating current to a hold open circuit comprising a hot surface igniter and the at least one coil, thereby holding the valve in the open position. In certain examples, the at least one coil comprises a direct current coil, and the method comprises converting the alternating current to a time-varying direct current which is supplied to the direct current coil. In other examples, the at least one coil comprises an alternating current coil. In certain examples, the step of manually activating the valve is performed until the hot surface igniter reaches at least the autoignition temperature of the cooking gas.

In accordance with a third aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly comprising a valve and at least one coil. The valve comprises a fluid inlet and a fluid outlet and is manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and the apparatus further comprises a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, and wherein when subjected to an alternating current of 120 V AC rms, the hot surface igniter reaches a surface temperature of at least 1400° F. in no more than eight seconds after the at least one coil is subjected to the threshold current.

In accordance with a fourth aspect of the present disclosure, a cooking gas safety apparatus is provided which comprises a valve assembly comprising a valve and at least one coil. The valve comprises a fluid inlet and a fluid outlet and is manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and the apparatus further comprises a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, and wherein when subjected to an alternating current of 120 V AC rms, the hot surface igniter reaches an autoignition temperature of at least one of butane, butane 1400, propane, and natural gas no more than eight seconds after the at least one coil is subjected to the threshold current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a gas valve assembly in a closed position, wherein the gas safety valve assembly comprises a valve that is manually actuatable to an open position and which also comprises a hold open coil that holds the valve assembly open when a threshold current through the coil is reached;

FIG. 2 is a cross-sectional view of the gas safety valve assembly of FIG. 1 in an open position.

FIG. 3 is a cross-sectional view of the gas safety valve assembly of FIG. 1 in the open position of FIG. 2 in which a tapered sleeve with a metering orifice has been removed;

FIG. 4 is a first example of a hold open circuit comprising a hot surface igniter and a direct current coil of a gas safety valve assembly;

FIG. 5 is a second example of a hold open circuit comprising a hot surface igniter and a direct current coil of a gas safety valve assembly;

FIG. 6 is a template circuit configured to energize a hot surface igniter to two different energization states and which may be provided with a number of different circuit components useful for providing various indications of the state of a burner and controlling its operation;

FIG. 7 is the template circuit of FIG. 6 modified to hold open a gas safety valve assembly comprising a direct current coil for holding the valve assembly open;

FIG. 8 is an example of a hold-open circuit comprising a hot surface igniter and an alternating current coil for holding open a gas safety valve assembly;

FIG. 9 is a illustrative depiction of voltage versus time for the capacitor input voltages in the hold-open circuit of FIG. 4 superimposed on the diode output voltage for the hold-open circuit;

FIG. 10A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniter in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 10B is a graph depicting simulation current versus time data for the hot surface igniter in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 10C is a graph depicting simulation voltage versus time data for the input voltage to the resistors in the hold open circuit of FIG. 4 when operating at full power;

FIG. 10D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 4 when operating at full power;

FIG. 11A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniter in the hold-open circuit of FIG. 4 when operating at reduced power;

FIG. 11B is a graph depicting simulation current versus time data for the hot surface igniter in the hold-open circuit of FIG. 4 when operating at reduced power;

FIG. 11C is a graph depicting simulation voltage versus time data for the input voltage to the resistors in the hold open circuit of FIG. 4 when operating at reduced power;

FIG. 11D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 4 when operating at reduced power;

FIG. 12A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniter of FIG. 5 when operating at full power;

FIG. 12B is a graph depicting simulation current versus time data for the hot surface igniter in the hold-open circuit of FIG. 5 when operating at full power;

FIG. 12C is a graph depicting simulation voltage versus time data for the input voltage to resistor 80 in the hold-open circuit of FIG. 5 when operating at full power;

FIG. 12D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 5 when operating at full power;

FIG. 13A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniter in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 13B is a graph depicting simulation current versus time data for the hot surface igniter in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 13C is a graph depicting simulation voltage versus time data for the input voltage to resistor 80 in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 13D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 5 when operating at reduced power;

FIG. 14 is a third example of a hold-open circuit comprising a hot surface igniter and a direct current coil of a gas safety valve assembly;

FIG. 15 is a fourth example of a hold-open circuit comprising a hot surface igniter and a direct current coil of a gas safety valve assembly;

FIG. 16A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniters in the hold open circuit of FIG. 14 and the hold open circuit of FIG. 15 when it is operating at full power;

FIG. 16B is a graph depicting simulation current versus time data for the input current to the hot surface igniters in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when it is operating at full power;

FIG. 16C is a graph depicting simulation voltage versus time data for the input voltage to the resistor in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when it is operating at full power;

FIG. 16D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 14 and the hold-open circuit of FIG. 15 when it is operating at full power;

FIG. 17A is a graph depicting simulation voltage versus time data for the input voltage to the hot surface igniter in the hold-open circuit of FIG. 15 when operating at reduced power;

FIG. 17B is a graph depicting simulation current versus time data for the hot surface igniter in the hold-open circuit of FIG. 15 when operating at reduced power;

FIG. 17C is a graph depicting simulation voltage versus time data for the input voltage to the resistor in the hold-open circuit of FIG. 15 when operating at reduced power; and

FIG. 17D is a graph depicting simulation current versus time data for the direct current coil in the hold-open circuit of FIG. 15 when operating at reduced power.

Like reference numerals refer to like parts in the figures.

DESCRIPTION

Described below are examples of gas safety valve apparatuses that comprise a valve assembly and a “hold open” circuit. The valve assembly comprises a valve and at least one coil that is energizable to hold the valve in the open position only when the at least one coil is subjected to a current that exceeds a threshold current value. The hold-open circuit ensures that the valve only admits gas to a burner when a user actuates a gas control knob or when the burner is lit. More specifically, the hold open circuit causes the valve to close if a hot surface igniter used to ignite the burner is not energized sufficiently to reach (or maintain) a surface temperature at or above the autoignition temperature of the cooking gas, thereby reducing the likelihood that gas will unintentionally flow to an unlit burner. In certain examples, the igniter is energized by a source of alternating current, and the at least one coil is a direct current coil that only holds the valve open when subjected to a threshold direct current. In accordance with such examples, the hold open circuit is configured to supply the threshold direct current to the at least one coil only when the igniter is supplied with a current sufficient to cause a surface of the igniter to reach an autoignition temperature of the cooking gas.

Referring to FIGS. 1-3, a cooking gas safety valve assembly 20 is provided. The cooking gas safety valve assembly 20 comprises valve 21, direct current coil 40, and magnetic core 42. Valve assembly 20 has a proximal end P and a distal end D spaced apart along a length axis l. The valve 21 comprises a rigid, metal housing 23 in which a gas inlet 22 and gas outlet 24 are defined and spaced apart along the radial axis r. The valve 21 has an open position (FIG. 2) in which the gas inlet 22 is in fluid communication with the gas outlet 24 and a closed position (FIG. 1) in which the gas inlet 22 and the gas outlet 24 are not in fluid communication. A tapered sleeve 28 with an inlet metering orifice 29 is provided and includes an outlet 31 through which gas may pass when a valve disk 36 is unseated (FIG. 2) from a shoulder 45 of an axial fluid passage 43. Not all of orifice 29 is visible in FIGS. 1 and 2, but gas inlet 22 is in fluid communication with orifice 29.

A shaft engagement surface 38 is provided on the valve disk 36 and is engaged by a shaft 44 (FIG. 2) that runs through the tapered sleeve 28 along the lengthwise (l) axis of the gas safety valve assembly 20. Shaft 44 is operatively connected to a gas knob stem 26 (the knob is removed in the figures) that is axially depressible in the distal direction along the lengthwise (l) axis of the cooking gas safety valve assembly 20. Depressing the gas knob stem 26 axially in the distal direction causes the shaft 44 to move the valve disk 36 distally along the lengthwise (l) axis and out of engagement with axial fluid passage 43 shoulder 45. The shaft 44 has a diameter along the radial axis r that is narrower than the diameter of the axial fluid passage 43 at shoulder 45, and distally of the shoulder 45. The fluid passage 43 has a diameter along the radial axis r that is larger than the diameter of the open area defined radially within shoulder 45. As a result, when valve disk 36 moves out of engagement with shoulder 45, gas exiting the outlet 31 of tapered sleeve 28 may exit the valve assembly gas outlet 24. Shaft 44 is biased in the proximal direction along the length axis l by spring 46 (FIG. 3). The gas knob stem 26 is also biased in the proximal direction along the length axis l due to its operative connection to shaft 44.

The valve disk 36 is connected to a distal valve shaft 32 which is in turn connected to a magnetic disk 30 that is housed in electromagnet housing 41. Electromagnet housing 41 houses a direct current coil 40 wrapped around a corresponding magnetic core 42. Multiple coils each wrapped around their own respective core may also be provided. The valve disk 36 is biased in the proximal direction along the length l axis by spring 34 which is attached to the proximal end of electromagnet housing 41. The distal valve shaft 32 runs through the spring 34 and through a hole (not shown) in the proximal end of the electromagnet housing 41. When the gas safety valve 21 is in the closed position (FIG. 1), the valve disk 36 is biased away from electromagnet housing 41 by biasing spring 34 and into engagement with shoulder 45 of axial fluid passage 43. When a user depresses gas knob stem 26 in the distal direction along the length l axis, the distal end 47 of shaft 44 (FIG. 3) engages the shaft engagement surface 38 of valve disk 36 and displaces the valve disk 36 in the distal direction along the length l axis to the open position of FIG. 2. The displacement of the valve disk 36 along the length l axis also displaces distal valve shaft 32 in the distal direction along the length l axis, thereby causing the magnetic disk 30 to be distally displaced into engagement with the magnetic core 42. When a threshold current is provided to the direct current coil 40, the resulting magnetic force will hold the valve's 21 magnetic disk 30 into engagement with the magnetic core 42 even if the user releases the gas knob stem 26. Without the magnetic force, releasing the gas knob stem 26 would cause the biasing force of spring 34 to urge valve disk 36 in the proximal direction along the length l axis and into engagement with the axial fluid passage channel shoulder 45, which in turn would cause shaft engagement surface 38 to urge shaft 44 in the proximal direction along the length l axis. As long as the direct current through the coil 40 remains above the threshold current characteristic of the gas safety valve assembly 20, the magnetic force will hold the valve's magnetic disk 30 into engagement with the magnetic core 42, thereby keeping the valve 21 in the open position of FIG. 2. The magnetic field generated by direct current coil 40 is strong enough to hold magnetic disk 30 into engagement with magnetic core 42 but is not strong enough to pull the magnetic disk 30 into engagement with magnetic core 42.

As mentioned previously, it would be desirable to modify the flame detection scheme typically used with cooking gas safety valve assembly 20 to shorten the duration of the manual actuation of gas knob stem 26 by the user prior to the valve disk 36 being held in the open position of FIG. 2 while still ensuring that gas is only supplied to the cooktop burner when a source of ignition is energized. As mentioned previously, the flame detection scheme typically uses a thermocouple to generate a direct current for the coil 40 when a flame is present.

In the examples that follow, instead of a spark igniter, the burner(s) with which cooking gas safety valve assembly 20 are used are ignited by a ceramic, hot surface igniter 52. Ceramic hot surface igniters useful in connection with the gas valve assemblies described herein include those described in U.S. patent application Ser. No. 16/366,479, the entirety of which is hereby incorporated by reference.

Although represented as a resistor in FIGS. 4-8, preferred ceramic hot surface igniters 52 useful in the gas heating systems described herein comprise a hot surface igniter having a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis. The igniter 52 comprises first and second ceramic tiles having respective outer surfaces. A conductive ink pattern is disposed between the first and second ceramic tiles. In certain examples, the igniter 52 has a thickness along the thickness axis of from about 0.047 inches to about 0.060 inches, preferably from about 0.050 to about 0.058 inches, and more preferably from about 0.052 inches to about 0.054 inches. See FIGS. 3A-3H and corresponding text of U.S. patent application Ser. No. 16/366,479.

The preferred ceramic hot surface igniters 52 described herein are generally in the shape of a rectangular cube and include two major facets, two minor facets, a top and a bottom. The major facets are defined by the first (length) and second (width) longest dimensions of the ceramic hot surface igniter body. The minor facets are defined by the first (length) and third (thickness) longest dimensions of the igniter body. The igniter bodies also include a top surface and a bottom surface which are defined by the second (width) and third (thickness) longest dimensions of the igniter body. The ceramic hot surface igniter 52 may have a positive or negative temperature coefficient of resistance. However, positive temperature coefficients of resistance are preferred.

In accordance with examples in which ceramic hot surface igniter 52 has a positive temperature coefficient of resistance, the igniter tiles are ceramic and preferably comprise silicon nitride. The conductive ink circuit is disposed between the tiles and generates heat when energized. The ceramic tiles are electrically insulating but sufficiently thermally conductive to reach the outer surface temperature necessary to ignite combustible mixtures of air and gases selected from natural gas, propane, butane, butane 1400 (a butane and air mixture with a heating value of 1400 Btu/ft³), and mixtures thereof, within the desired period of time.

As described in greater detail below, in certain examples, the ceramic tiles comprise silicon nitride, ytterbium oxide, and molybdenum disilicide. In the same or other examples, the conductive ink circuit comprises tungsten carbide, and in certain specific implementations, the conductive ink additionally comprises ytterbium oxide, silicon nitride, and silicon carbide.

In certain examples, when subjected to a potential difference of 120V AC (rms), the ceramic hot surface igniters 52 described herein reach a surface temperature of at least 1400° F., preferably no less than 1800° F., more preferably no less than 2100° F., and even more preferably no less than 2130° F. These temperatures are preferably reached in no more than eight seconds, more preferably reached in no more than six seconds, and still more preferably, reached in no more than four seconds after the 120V AC (rms) potential difference is applied.

In the same or additional examples, the surface temperature of the ceramic hot surface igniters herein does not exceed 2600° F., preferably does not exceed 2550° F., more preferably does not exceed 2500° F., and still more preferably 2450° F. at any time after a full wave 132V AC (rms) potential difference is applied to the igniter, including after a steady-state temperature is reached.

In the same or other examples of ceramic hot surface igniters in accordance with the present disclosure, when subjected to a potential difference of 102V AC (rms), the ceramic hot surface igniters described herein reach a surface temperature of at least 1400° F., preferably at least 1800° F., and still more preferably at least 2100° F. in no more than seventeen, preferably more than ten, and more preferably no more than about seven seconds after the 102V AC (rms) potential difference is first applied. These temperatures are preferably reached in no more than four seconds and are more preferably reached in no more than three seconds.

In the same or additional examples, the thickness of the conductive ink circuit of the hot surface igniter (taken along the thickness axis) is not more than about 0.002 inches, preferably not more than about 0.0015 inches, and more preferably, not more than about 0.0009 inches. In the same or additional examples, the thickness of the conductive ink circuit (taken along the thickness axis) is not less than about 0.00035 inches, preferably not less than about 0.0003 inches, and more preferably, no less than about 0.0004 inches.

The hot surface igniters 52 of the present disclosure also preferably have a green body density of at least 50 percent of theoretical density, more preferably, at least 55 percent, and still more preferably at least 60 percent of theoretical density.

As discussed in U.S. patent application Ser. No. 16/366,479, ceramic hot surface igniters 52 used in the gas heating systems described herein are prepared by sintering ceramic compositions. In certain examples, post-sintering, the tiles used to form the igniter 52 (not including conductive ink circuit) have a room temperature resistivity that is no less than 10¹² Ω-cm, preferably no less than 10¹³ Ω-cm, and more preferably, no less than 10¹⁴ Ω-cm. In the same or other examples, the tiles have a thermal shock value in accordance with ASTM C-1525 of no less than 900° F., preferably no less than 950° F., and more preferably, no less than 1000° F.

In other examples, the conductive ink comprising the conductive ink circuit has a (post-sintering) room temperature resistivity of from about 1.4×10⁻⁴ Ω·cm to about 4.5×10⁻⁴ Ω·cm, preferably from about 1.8×10⁻⁴ Ω·cm to about 4.1×10⁻⁴ Ω·cm, and more preferably from about 2.2×10⁻⁴ Ω·cm to about 3.7×10⁻⁴ Ω·cm. In the case of a material with a constant cross-sectional area along its length, resistivity ρ at a given temperature T is related to resistance R at the same temperature Tin accordance with the well-known formula:

R(T)=ρ(T)(I/A),  (1)

where

-   -   ρ=resistivity of conductive circuit material (Ω-cm) at         temperature T;     -   R=Resistance in ohms (Ω) at temperature T;     -   T=Temperature (° F. or ° C.);     -   A=cross-sectional area (cm²) of conductive ink circuit         perpendicular to the direction of current flow; and     -   l=total length (cm) of the conductive ink circuit along the         direction of current flow.

In the case of a cross-sectional area that varies along the length of the conductive circuit, the resistance may be represented as:

$\begin{matrix} {R = {{\rho(T)}{\int_{0}^{L}\frac{dl}{A}}}} & (2) \end{matrix}$

-   -   where, L=total length of circuit along direction of current flow         (cm), and the remaining variables are as defined for equation         (1).

In certain examples, the ceramic bodies comprising the ceramic hot surface igniters 52 herein preferably comprise silicon nitride and a rare earth oxide sintering aid, wherein the rare earth element is one or more of ytterbium, yttrium, scandium, and lanthanum. The sintering aids may be provided as co-dopants selected from the foregoing rare earth oxides and one or more of silica, alumina, and magnesia. A sintering aid protective agent is also preferably included which also enhances densification. A preferred sintering aid protective agent is molybdenum disilicide. The rare earth oxide sintering aid (with or without the co-dopant) is preferably present in an amount ranging from about 2 to about 15 percent by weight, more preferably from about 8 to about 14 percent by weight, and still more preferably from about 12 to about 14 percent by weight of the ceramic body. Molybdenum disilicide is preferably present in an amount ranging from about 3 to about 7 percent, more preferably from about 4 to about 7 percent, and still more preferably from about 5.5 to about 6.5 percent by weight of the ceramic body. The balance is silicon nitride.

The conductive ink circuit is preferably printed onto the face of one of the ceramic tiles to yield a ceramic hot surface igniter(post-sintering) room temperature resistance (RTR) of from about 60Ω to about 120Ω, preferably from about 70Ω to about 110Ω, and more preferably from about 80Ω to about 100Ω. At the same time, the ceramic hot surface igniter high temperature resistance (HTR) over the temperature range 2138° F. to 2700° F. is generally from about 300Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450Ω.

The conductive ink in the igniter 52 should comprise tungsten carbide in an amount ranging from about 20 to about 80 percent, preferably from about 30 percent to about 80 percent, and more preferably from about 70 to about 75 percent by weight of the ink. Silicon nitride is preferably provided in an amount ranging from about 15 to about 40 percent, preferably from about 15 to about 30 percent, and more preferably from about 18 to about 25 percent by weight of the ink. The same sintering aids or co-dopants described for the ceramic body are also preferably included in an amount ranging from about 0.02 to about 6 percent, preferably from about 1 to about 5 percent, and more preferably from about 2 to about 4 percent by weight of the ink.

In the examples of cooking gas safety apparatuses described herein, a hot surface igniter 52 is used to ignite cooking gas supplied to a burner, and the flow of gas to the burner is regulated by a cooking gas safety valve assembly 20 that is held open only when the current supplied to the hot surface igniter is sufficient for the igniter to reach the autoignition temperature of the cooking gas. The “autoignition temperature” is the lowest temperature at which a gas-air mixture will ignite and continue to burn. In preferred examples, the igniter 52 is also operable in a full power and a reduced power mode. During ignition, the igniter 52 would operate at full power. Following ignition, the igniter would operate at reduced power, albeit a power sufficient to heat the igniter to at least the autoignition temperature of the cooking gas.

Referring to FIG. 4, a portion of a cooking gas safety apparatus is depicted. The cooking gas safety apparatus comprises a hold open circuit 50 and cooking gas safety valve assembly 20, which includes direct current coil 40 (shown in the figure). The valve assembly 20 is manually actuatable to an open position (FIG. 2) using gas knob stem 26 as described previously. When the direct current coil 40 is energized to a current that exceeds a threshold direct current while the valve disk 36 is in the open position of FIG. 2, the magnetic force of the direct current coil 40 holds the valve disk 36 open by holding magnetic disk 30 into engagement with magnetic core 42 without the need for the user to continue to depress gas knob stem 26. In the case of a time-varying current, the threshold direct current is the RMS value of the time-varying current.

The hold open circuit 50 includes hot surface igniter 52 and direct current coil 40. As shown in the figure, the hot surface igniter 52 is in electrical communication with the direct current coil 40 such that when the direct current coil 40 is subjected to a current having the threshold current value, a surface of the igniter 52 reaches at least an autoignition temperature of the cooking gas. Providing an igniter 52 that only reaches the gas autoignition temperature when the direct current coil 40 is at or below threshold current better ensures that gas is shut-off to the burner when the igniter is not hot enough to ignite the cooking gas. As a result, flame detection devices such as thermocouples which have significant dead time or lag time may be eliminated, which significantly reduces the amount of time during which the user must depress the gas knob stem 26 in the distal direction along the length l axis to keep the gas valve assembly in the open condition (of FIG. 2).

The hot surface igniter 52 is powered by an alternating current source 51. In accordance with the example of FIG. 4, the alternating current supplied by alternating current source 51 to direct current coil 40 is converted to a time-varying direct current. As used herein, “direct current” refers to a current having one polarity. A “direct current” may have a constant or time-varying value as long as it has one polarity. Because alternating current source 51 has two polarities, the hold-open circuit 50 is configured to store electric potential when the alternating current source cycle is one polarity and to make the electric potential available for use by the direct current coil 40 when the alternating current source cycle is the opposite polarity. Although not shown in FIG. 4, another switch would be provided to selectively energize the hold-open circuit 50 in response to the depression of gas knob stem 26 in the distal direction along the length l axis (FIG. 2). Thus, although not specifically depicted, it is understood that the alternating current source 51 is in selective electrical communication with the hot surface igniter 52 and the direct current coil 40.

As shown in FIG. 4, the hot surface igniter 52 is in a series-parallel combination with the direct current coil 40. The terms “series-parallel” and “parallel-series” refer to components that are not strictly in a series or parallel relationship with one another. The term “series” as used to describe the relationship between two components of an electrical circuit means one current flows in turn through each of the components. The term “parallel” as used to describe the relationship between two components of an electrical circuit means that the current divides between the components and then later reunites. Referring to FIG. 4, a portion of the current flowing through igniter 52 will flow through the direct current coil 40, another portion of the current flowing through igniter 52 will flow through resistor 56, and the two currents will re-unite.

In FIG. 4 the alternating current supplied to the hot surface igniter 52 is rectified, and preferably half-wave rectified. As is known in the art, diodes allow current of only one polarity to flow. Diode 64 is in a series-parallel combination with hot surface igniter 52 as a portion of the current flowing through diode 64 during the portion of the AC cycle in which the diode is forward biased will also flow through the hot surface igniter 52. Diode 64 is not placed directly in series with hot surface igniter 52 because the current flowing from diode 64 to igniter 52 would drop to zero during each half AC cycle, causing the direct current coil 40 to release the valve disk 36 to the closed position of FIG. 1 when the current crosses the zero pole. As a result, one more capacitors are provided which charge when diode 64 is forward-biased and discharge when diode 64 is reverse-biased. The diode 64 voltage and current rating are preferably selected to balance cost with the circuit 50 lifetime as lower voltage or current ratings will tend to decrease the lifetime of circuit 50.

A half-wave rectified voltage such as that provided by diode 64 is a time-varying, unidirectional voltage and has the appearance of an AC sine wave superimposed on a DC signal, which is known as a “ripple.” A ripple has a characteristic factor called the “ripple factor” which is the ratio of the root-mean-square (RMS) value of the AC component to the mean value of the total. A single phase, half-wave rectified signal such as the output of diode 64 has a ripple factor of 1.21. As known to those skilled in the art, an RMS value of a time-varying signal is the square root of the mean value of a squared function. In the context of a time-varying current or voltage, the respective RMS current or voltage value is the DC value that has an effect equivalent to the time-varying value. The RMS voltage and current can be calculated from equations (2a) and 2(b), respectively:

$\begin{matrix} {V_{rms} = \sqrt{\frac{1}{{T2} - {T1}}{\int_{T1}^{T2}{{{v(t)}}^{2}{dt}}}}} & \left( {2a} \right) \end{matrix}$

-   -   where, v(t) is a periodic, time-varying voltage (volts) having a         period of T₂−T₁ (seconds);     -   T1=time value (seconds) at the beginning of a period;     -   T2=time value (seconds) at the end of the period beginning at         T1; and     -   v_(rms) is the root-mean-square voltage (volts) of the function         v(t)

$\begin{matrix} {i_{rms} = \sqrt{\frac{1}{{T2} - {T1}}{\int_{T1}^{T2}{\left. {i(t)} \middle| {}_{2}{dt} \right.}}}} & \left( {2b} \right) \end{matrix}$

-   -   where, i(t) is a periodic, time-varying current (Amperes) having         a period of T₂−T₁ (seconds);     -   T1=time value (seconds) at the beginning of a period;     -   T2=time value (seconds) at the end of the period beginning at         T1; and     -   i_(rms) the root-mean-square voltage (volts) of the function         i(t)

In the example of FIG. 4, two capacitors 58 and 60 are provided. Capacitor 58 and 60 help to smooth the direct current ripple voltage and increase the root mean square (RMS) voltage seen by the igniter 52 and the direct current coil 40 after rectification. Capacitor 60 is in selective electrical communication with hot surface igniter 52 and direct current coil 40. Switch 62 is in series with capacitor 60. When switch 62 is open, capacitor 60 is disconnected from the hold open circuit 50 and is not in electrical communication with either hot surface igniter 52 or direct current coil 40, i.e., only capacitor 58 reduces the ripple factor. When switch 62 is closed and in contact with pole 63, capacitor 60 is in electrical communication with both hot surface igniter 52 and direct current coil 40.

Referring first to the case when switch 62 is open, when the diode 64 is forward biased, capacitor 58 will charge and will draw current until reaching its saturation voltage. When the AC source voltage begins to drop from its maximum, capacitor 58 will begin to discharge when the AC source voltage falls below the capacitor 58 saturation voltage. Thus, when the AC source 51 switches polarity and diode 64 is reverse biased, the capacitor 58 will continue to discharge and supply current to hot surface igniter 52 and direct current coil 40. The result is that the hot surface igniter 52 and the direct current coil 40 effectively see a smoothed ripple, i.e., their voltages are equivalent to an AC voltage sinewave superimposed on a DC voltage signal. FIG. 9 depicts how capacitor 58 alone or in parallel with capacitor 60 (when switch 62 is closed) smooths the ripple voltage produced by diode 64. The rectified waveform in FIG. 9 is the output voltage signal from diode 64, which is also the input voltage to hot surface igniter 52 and at node N₅₂. During the portion of the wave form where the diode 64 output voltage is increasing, capacitor 58 is charging (as is capacitor 60 if switch 62 is closed) until it reaches its saturation voltage or until the AC source reaches its peak voltage. Thus, when capacitor 58 is charging, the hot surface igniter 52 input voltage tracks the AC wave form from AC source 51. As the AC source reaches its peak voltage and begins to fall below the capacitor 58 saturation voltage, capacitor 58 begins to discharge and supplies current to hot surface igniter 52 as indicated by the upper line segments in FIG. 9. Once the capacitor 58 voltage drops below the AC source voltage, capacitor 58 again begins to charge. As a result, hot surface igniter 52 sees the voltage represented by the upper graph in FIG. 9 instead of seeing the rectified voltage output from diode 64, thereby smoothing the ripple of the rectified wave form. The resulting voltages and currents seen by the hot surface igniter 52 and the direct current coil 40 are time-varying direct current voltages and currents, which enable the direct current coil 40 to hold the valve disk 36 (FIG. 2) open despite the AC source reversing polarity every half cycle. As the total capacitance of circuit 50 increases, it “smooths” or dampens the ripple. When switch 62 is closed, the total capacitance is the sum of the capacitances of capacitor 58 and capacitor 60. When switch 62 is open, the total capacitance is the capacitance of capacitor 58. The smoothing effect of the capacitance is indicated by equation (2c) which shows that as the total capacitance C_(total) increases, the spread (ΔV) between the maximum and minimum voltages seen by hot surface igniter 52 decreases:

ΔV=0.7i/((f)C _(total))  (2c)

-   -   where, ΔV=the difference in voltage between adjacent peaks in         the voltage versus time signal (volts);     -   i=the DC load current seen by hot surface igniter 52 (amperes);         and     -   f=ripple frequency (Hz (generally 120 Hz for full-wave or 60 Hz         for half-wave)).

In equation (2c), 0.7 is the complement of the rectifier-current duty cycle, which is assumed to be 0.3. As the capacitance of capacitor 58 increases, the igniter 52 input voltage at node N₅₂ shows less ripple (becomes flatter) in both the full and reduced power modes (described below). As the capacitance of capacitor 60 increases, the igniter 52 input voltage at node N₅₂ shows less ripple during the full power only, and igniter 52 will heat to a higher temperature. Also, as the capacitance of capacitor 60 increases the likelihood of stressing the components of circuit 50 beyond their ratings increase. Conversely, when circuit 50 is in reduced power mode, as the capacitance of capacitor 60 decreases, the igniter 52 input voltage at node N₅₂ will show more ripple (become “less flat”), and the RMS current through igniter 52 will decrease, causing igniter 52 to reach a lower steady-state temperature. The direct current coil 40 tends to have a much lower resistance and inductance than the other circuit components. Thus, the selection of those properties for the coil 40 tends to be less critical to the overall performance of circuit 50.

When switch 62 is closed, the hot surface igniter 52 is in full-power mode. When switch 62 is open, hot surface igniter 52 is in reduced power mode. Full power mode is preferably used during an ignition operation. Reduced power mode is preferably used during a cooking operation and provides a means of reigniting the cooking gas in the event of a flame out. When switch 62 is closed, capacitors 58 and 60 act as a single capacitor having a total capacitance that equals the sum of each of their respective capacitances, meaning that the parallel combination is equivalent to a single capacitor having a capacitance equal to the sum of both capacitances. The capacitance values of capacitors 58 and 60 will affect the percentage of full power that is achieved during reduced power operation. In certain examples, releasing the gas valve stem 26 after the direct current coil 40 has latched in the open position of FIG. 2 will cause switch 62 to open and place circuit 50 in a reduced power mode. In certain examples, the power provided to igniter 52 in the reduced power mode is from about 70 percent to about 90 percent, preferably from about 75 percent to about 85 percent, and more preferably from about 78 percent to about 82 percent of the power provided to igniter 52 in a full power mode.

The power dissipated in surface igniter 52 is proportional to the total capacitance of capacitors 58 and 60 in full-power mode and capacitor 58 in reduced power mode. Thus, the ratio of igniter power dissipation in reduced-power mode to the igniter power dissipation in full-power mode decreases as the capacitance of capacitor 60 increases relative to the capacitance of capacitor 58. As is the case with reduced power mode, while the diode 64 is forward-biased, the capacitors 58 and 60 will charge until reaching their saturation voltages. Once the capacitors are saturated, no current will flow to them until the AC source 51 voltage drops below their saturation voltages (which may differ between capacitors 58 and 60). As the output voltage from diode 64 falls below either capacitor's saturation voltage (or falls below the peak source voltage if it is less than the saturation voltage), that capacitor will begin to discharge, causing current to flow from the capacitor 58 and/or 60 through the igniter 52 and to direct current coil 40. When the diode 64 is reverse-biased, no current from the AC source 51 will flow through it. However, capacitors 58, 60 will continue to provide current to the igniter 52 and the direct current coil 40.

In hold-open circuit 50 of FIG. 4, the hot surface igniter 52 is not directly in series with the direct current coil 40 because the threshold current required to hold the valve assembly 20 open is less than the hot surface igniter 52 current required for the igniter surface to reach the autoignition temperature of the cooking gas. Resistor 56 is a shunt resistor that makes circuit 50 more sensitive and more responsive by shunting current away from direct current coil 40, which causes direct current coil 40 to shut off—and valve 21 to close—at a higher current than would otherwise be required in the absence of resistor 56. Especially in full power mode, the igniter 52 may receive significantly more current than the threshold current for direct current coil 40 to magnetically hold open the valve assembly 20 (FIGS. 1-3). Thus, the shunt resistor 56 bypasses some of this current around the direct current coil 40. As the resistance of resistor 56 increases, the direct current coil 40 will receive a larger portion of the current received by igniter 52, in which case a lower igniter 52 current will be required to reach the trigger current of the direct current coil 40. Conversely, as the resistance of resistor 56 decreases, the direct current coil 40 will receive a smaller portion of the current received by igniter 52, in which case a higher igniter 52 current will be required to reach the trigger current of the direct current coil 40. Thus, the resistance of shunt resistor 56 may be selected to provide a margin of safety between the igniter 52 current at which the igniter 52 reaches the cooking gas autoignition temperature and the trigger current at which the direct current coil 40 holds open the valve 21. Resistor 54 is provided to provide an additional voltage drop between the igniter 52 and the coil 40. At a given resistance value for resistor 56, increasing the resistance of resistor 54 will cause a lower portion of the current received by igniter 52 to be received by direct current coil 40, while decreasing the resistance of resistor 54 will have the opposite effect. Fuse 66 provides an extra layer of protection in the event that the shunt resistor 56 fails. The higher the current rating of fuse 66, the longer the circuit 50 will take to turn off in the event of a catastrophic failure. However, too low a rating may cause the fuse to undesirably blow during normal circuit 50 operation.

The hold open circuit of FIG. 4 can be described as several equivalent circuits comprising various series and parallel combinations of components. Fuse, 66, resistor 54 and direct current coil 40 form a first series combination that forms a first parallel combination with shunt resistor 56. The first parallel combination forms a second series combination with hot surface igniter 52.

Capacitors 58 and 60 form a second parallel combination with one another, and the second parallel combination forms a third parallel combination with the second series combination. The third parallel combination forms a third series combination with diode 64.

The hold open circuit 50 is preferably designed to operate at AC source 51 voltages ranging from 90 V AC (rms) to about 135V AC (rms), preferably from about 110V AC (rms) to about 130 V AC (rms), and more preferably from about 115V AC (rms) to about 125 V AC (rms) and supply sufficient current for igniter 52 to reach the autoignition temperature of the cooking gas. In certain examples, hot surface igniter 52 is designed to have a high temperature resistance (i.e., a resistance at the ignition temperature of the cooking gas) that ranges from about 330Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450 a Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Direct current coil 40 also has an inductance ranging from about 0.005 mH to about 0.010 mH, preferably from about 0.006 mH to about 0.009 mH, and more preferably from about 0.007 mH to about 0.008 mH.

Capacitors 58 and 60 may have exemplary values ranging from about 15 μF to about 30 μF, preferably from about 18 μF to about 25 μF, and more preferably from about 20 μF to about 24 μF. Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Resistors 54 and 56 may have exemplary resistance values ranging from about 20Ω to about 40Ω, preferably from about 25Ω to about 35Ω, and more preferably from about 28Ω to about 32Ω. Fuse 66 may be rated, for example, for about 0.5 A to about 1.5 A, preferably from about 0.6 A to about 1.3 A, and more preferably from about 0.8 A to about 1.2 A.

Example 1

A hold-open circuit 50 as shown in FIG. 4 is provided. Hot surface igniter 52 comprises a silicon ceramic body with a rare earth sintering aid and a molybdenum disilicide sintering aid protective agent. The rare earth oxide sintering aid is present in an amount ranging from about 12 to about 14 percent of the ceramic body by weight. The molybdenum disilicide sintering aid protective agent is present in an amount ranging from about 5.5 percent to about 6.5 percent by weight of the ceramic body. The balance (79.5 percent to about 82.5 percent by weight of the ceramic body) is silicon nitride. The conductive ink in the igniter 52 comprises tungsten carbide in an amount ranging from about 70 to about 75 percent by weight of the ink. Silicon nitride is provided in an amount ranging from about 18 to about 25 percent by weight of the ink. The same sintering aids or co-dopants described for the ceramic body are also included in an amount ranging about 2 to about 4 percent by weight of the ink. The thickness of the conductive ink circuit of the hot surface igniter (taken along the thickness axis) is not more than about 0.002 inches, preferably not more than about 0.0015 inches, and more preferably, not less than about 0.0004 inches and not more than about 0.0009 inches.

Capacitors 58 and 60 have respective capacitance values of 22 μF. Resistors 54 and 56 have resistance values of 3052. Direct current coil 40 has an inductance value of 0.0074 mH. The circuit is simulated with a 120 VAC (rms) 60 Hz voltage source signal. FIG. 10A depicts the input voltage at igniter 52 in volts versus time. Circuit 50 is operated in a full power mode in which switch 62 is closed. The capacitors 58 and 60 each have a capacitance of 22 μF and together act like a single capacitor with a capacitance of 44 μF. The voltage signal seen by the igniter has an rms value of 130V, higher than that of the AC source signal owing to the smoothing effect of the capacitors on the ripple produced by diode 64. FIG. 10B shows the current through igniter 52 and has a similar pattern with an rms value of 267 mA. At these voltage and current values, the igniter high temperature resistance would be about 471Ω, and the estimated igniter surface temperature would reach about 2430° F. at steady-state.

FIGS. 10C and 10D show the voltage output from the igniter 52 and the current received by direct current coil 40, respectively. As would be expected, the waveforms have a shape similar to those of FIGS. 10A and 10B. However, the rms output voltage from the igniter 52 is 4.4V. The rms current to the direct current coil 40 is 201 mA, which is sufficient to latch direct current coil 40 and cooking gas safety valve assembly 20 in the open position of FIG. 2.

FIGS. 11A-11D are simulation results in reduced power mode, i.e., with switch 62 open. As mentioned previously, a reduced power mode is preferably used following ignition and during a cooking operation as a way of preventing flame outs while reducing energy costs and extending the life of igniter 52 relative to operating igniter 52 in a constant full power mode. FIG. 11A shows the igniter 52 input voltage. The wave form is similar to that of FIG. 10A. However, the igniter 52 input rms voltage is 109 V. Referring to FIG. 11B, the average igniter 52 rms current is 245 mA. The high temperature resistance of igniter 52 would be about 429Ω.

FIGS. 11C-11D show the reduced power mode case for the igniter 52 output voltage and the direct current coil 40 current. The average igniter 52 output rms voltage value is 4.1V. The average direct current coil 40 rms current is 185 mA. At these estimated current and voltage values, the igniter 52 would reach a surface temperature of about 2150° F. at steady-state. Referring to FIG. 5, a portion of another exemplary cooking gas safety apparatus is depicted. The cooking gas safety apparatus comprises a hold open circuit 70 and cooking gas safety valve assembly 20, which includes direct current coil 40 (shown in the figure). Like hold open circuit 50, hold open circuit 70 is powered by a source of alternating current 71 and converts it to a time-varying direct current so that known gas taps with direct current coils like coil 40 may be used. Although not shown, an additional switch would be provided to selectively connect the source of alternating current 71 to the remainder of the hold open circuit 70 when a user actuates the valve assembly 20 by depressing and turning the gas knob stem 26. Hot surface igniter 52 is in selective electrical communication with direct current coil 40 depending on the state of Zener diode 72 (described below).

Hold open circuit 50 of FIG. 4 uses two parallel capacitors, one of which is selectively connectable to the circuit 50 to provide full and reduced power modes for the igniter 52. In contrast, hold open circuit 70 of FIG. 5 uses two parallel resistors 82 and 84, one of which (84) is selectively connectable to the hold open circuit (via switch 86) to provide full and reduced power modes. Resistors 82 and 84 are in parallel with one another when switch 86 is closed. When switch 86 is open, resistor 84 is not in electrical communication with the source of alternating current 71 and is effectively out of the hold open circuit 70. The parallel combination of resistors 82 and 84 is equivalent to a single resistor with a resistance that equals the product of their resistances divided by the sum of their resistances. The combined resistance will always be lower than each of the individual resistances. Thus, closing switch 86 places circuit 70 in full power mode, and opening switch 86 places circuit 70 in reduced power mode. Full power mode is preferably used during an ignition operation. Reduced power mode is preferably used during a cooking operation and provides a means of reigniting the cooking gas in the event of a flame out. In certain examples, the power provided to igniter 52 in the reduced power mode is from about 70 percent to about 90 percent, preferably from about 75 percent to about 85 percent, and more preferably from about 78 percent to about 82 percent of the power provided to igniter 52 in a full power mode.

In certain examples, releasing the gas valve stem 26 after the direct current coil 40 has latched in the open position of FIG. 2 will cause switch 86 to open (to place circuit 70 in a reduced power cooking mode). Otherwise, switch 86 will remain closed.

Direct current coil 40 is in series with a Zener diode 72 and fuse 78 to form a first series combination. The first series combination forms a first parallel combination with resistor 80. When switch 86 is closed, the second parallel combination of resistors 82 and 84 is in series with the first parallel combination to form a second series combination. The second series combination forms a third series combination with hot surface igniter 52. The third series combination and capacitor 74 form a third parallel combination that is in series with diode 76 and fuse 88.

When switch 86 is open, the second series combination consists of the first parallel combination and resistor 82 alone (i.e., without resistor 84). Thus, when switch 86 is closed, hot surface igniter 52 is in series with an equivalent circuit component having an overall resistance lower than when switch 86 is open. This means that more voltage is available for the igniter 52, and hence, it draws more power. Resistor 82 determines how hot igniter 52 will get in reduced power mode and impacts the igniter 52 temperature in full power mode.

When switch 86 is closed, resistor 84 allows more current to flow through the circuit 70, causing the igniter 52 to get hotter in full power mode. Increased values of the resistance of resistor 84 will tend to decrease the power dissipated by igniter 52 in full power mode, whereas decreased resistance values of resistor 84 will tend to increase the power dissipated by igniter 52 in full power mode.

As with hold open circuit 50, hold open circuit 70 includes a diode 76 to half-wave rectify the AC power source 71. Diode 76 is preferably selected to have a voltage rating that balances cost and the desired lifetime of circuit 70. Higher voltage rating diodes tend to be more expensive, but as the voltage rating of diode 76 decreases, the lifetime of circuit 70 decreases. Because of diode 76 and as with circuit 50, a ripple is also present in circuit 70. Here, capacitor 74 is placed in a series-parallel relationship to the diode 76 and the hot surface igniter 52 to smooth the ripple voltage and reduce the ripple factor. Capacitor 74 is not selectively connected to the hold open circuit 70 but rather remains in electrical communication with the hot surface igniter 52 and direct current coil 40 at all times. When diode 76 is forward-biased, capacitor 74 will charge until it reaches its saturation voltage. Once the capacitor is at its saturation voltage, if the AC source 71 voltage drops below the saturation voltage, capacitor 74 will begin discharging until the AC voltage exceeds the capacitor 74 voltage, at which point capacitor 74 will begin charging again. In general, increasing values of the capacitance of capacitor 74 will flatten the ripple in the igniter 52 input voltage at node N₅₂ in both the full and reduced power modes of operation and will also lower the AC supply voltage at which the valve assembly 20 releases to the closed position of FIG. 1, i.e., at a lower supply voltage the direct current coil 40 will still see the threshold current necessary to hold the valve disk 36 in the open position of FIG. 2. The power dissipated by the igniter 52 will increase in both the full and reduced power modes at higher capacitance values relative to lower ones.

Resistor 80 acts as a current set resistor. As the current through igniter 52 increases, the voltage at resistor 80 increases. When the voltage at resistor 80 reaches the breakdown voltage of Zener diode 72, direct current coil 40 will receive current. Fuse 78 provides an extra layer of protection for direct current coil 40 in the event that resistor 80 fails. At excessively higher current ratings, direct current coil 40 may fail to close when circuit 70 fails. If the fuse 78 current rating is too low, the direct current coil 40 may shut valve 21 during normal operation. Fuse 88 provides overall circuit protection.

Instead of using a current limiting resistor in series with the direct current coil 40—as in the case of hold open circuit 50—hold open circuit 70 includes a Zener diode 72 in series with direct current coil 40. The Zener diode 72 is operated in reverse-biased mode. When the voltage input to the Zener diode drops below the Zener breakdown voltage, it stops allowing current to flow to the direct current coil 40, causing it to release valve magnetic disk 30 so that it is biased to the closed position of FIG. 1. Thus, the Zener diode 72 acts as a low voltage switch that ensures the direct current coil 40 does not hold open the valve disk 36 when the igniter 52 is not hot enough to ignite cooking gas.

Hold open circuit 70 beneficially includes several features that prevent valve assembly 20 from remaining open in the case of circuit component failures. For example, if diode 76 fails by shorting, alternating current will flow through the direct current coil 40, causing it to release. Because the valve assembly 20 is a hold open valve assembly, gas will cease to flow to the burner(s) unless and until manual actuation of the gas knob stem 26 is performed. If diode 76 fails open, the direct current coil 40 will cease to generate a magnetic field, and valve assembly 20 will fail to the closed position of FIG. 1, thereby shutting of gas flow to the burner(s).

If capacitor 74 fails by shorting, all the current will flow through capacitor 74 causing fuse 88 to blow and the valve assembly 20 to fail to the closed position of FIG. 1. If capacitor 74 fails open, at 60 Hz on the AC signal, the current to the direct current coil will drop to zero, causing the valve assembly 20 to fail to the closed position of FIG. 1.

If igniter 52 fails by shorting, too much current will flow though the circuit 70 and fuse 78 will blow, causing the valve assembly 20 to fail to the closed position of FIG. 1. If igniter 52 fails open, no current will reach the direct current coil 40, again causing the valve assembly 20 to shut off the flow of gas to the burner(s) by failing to the closed position of FIG. 1.

If Zener diode 72 fails by shorting, the current through the direct current coil 40 will increase quickly and significantly causing fuse 78 to blow and valve assembly 20 to fail to the closed position of FIG. 1. If the Zener diode 72 fails open, no current can reach the direct current coil 40 causing valve assembly 20 to fail to the closed position.

If the shunt resistor 80 fails by shorting, no current will reach the direct current coil 40 causing it to release the valve disk 36 and shut off gas flow to the burner(s). If the shunt resistor 80 fails open, the current to the direct current coil 40 will increase precipitously, causing fuse 78 to blow, and valve assembly 20 to fail closed.

If resistor 82 fails open with switch 86 open, nothing will happen because there will be no closed path for current flow through direct current coil 40. If resistor 82 fails by shorting with switch 86 open or closed, igniter 52 will see a large spike in current, causing it to heat up significantly, which could lead to an igniter 52 failure. If resistor 82 fails open with switch 86 closed, igniter 52 will be operable in reduced power mode only. If resistor 84 fails open with switch 86 open or closed, igniter 52 will operate in reduced power mode only. If resistor 84 fails closed with switch 86 closed, the igniter 52 will see a large spike in current, causing it to heat up significantly, which may lead to an igniter 52 failure.

The capacitance and resistance values of the various components of hold-open circuit 70 may be selected to achieve the desired circuit 70 operation. In general, if it is desired to make the direct current coil 40 hold open sooner upon actuating the gas knob stem 26, the resistance of resistor 80 may be increased. Increasing the resistance of resistor 80 will increase the input voltage to Zener diode 72 and resistor 80, plus it will cause relatively more of the total current going through igniter 52 to go through the direct current coil.

If it is desired to operate the igniter 52 at a higher temperature, the resistance values of resistors 82 and 84 may be decreased, which will increase the current flowing through igniter 52. At the same time, or alternatively, the capacitance value for capacitor 74 may be increased. Increasing the capacitance of capacitor 74 provides more stored electrical energy when capacitor 74 discharges (i.e., when the output voltage from diode 76 falls below the saturation voltage of capacitor 74). As a result, the rms voltage seen by the igniter 52 increases, thereby increasing its surface temperature.

The hold open circuit 70 is preferably designed to operate at AC voltages ranging from 90 V AC (rms) to about 135V AC (rms), preferably from about 110V AC (rms) to about 130 V AC (rms), and more preferably from about 115V AC (rms) to about 125 V AC (rms). In certain examples, hot surface igniter 52 is designed to have a high temperature resistance (i.e., a resistance at the ignition temperature of the cooking gas) that ranges from about 330Ω to about 500Ω, preferably from about 400Ω to about 480Ω, and more preferably from about 430Ω to about 450Ω.

At the same time, capacitor 74 may have exemplary capacitance values ranging from about 60 μF to about 80 μF, preferably from about 65 μF to about 75 μF, and more preferably from about 66 μF to about 70 μF. Direct current coil 40 has a threshold (rms) current ranging from about 30 mA to about 90 mA, preferably from about 40 mA to about 80 mA, and more preferably from about 50 mA to about 70 mA. Direct current coil 40 also has an inductance ranging from about 0.005 mH to about 0.010 mH, preferably from about 0.006 mH to about 0.009 mH, and more preferably from about 0.007 mH to about 0.008 mH. In addition, at higher capacitance values for capacitor 74 the igniter 52 voltage at node N₅₂ will show a smaller ripple (become “flatter”) in both power modes. This in turn will decrease the currents in the circuit 70 along with the steady-state temperature of igniter 52, and valve 21 may not remain open during lower power mode operation. The resistance and impedance of direct current coil 40 will typically be much lower than that of the other circuit components, and will be effectively negligible.

At the same time resistor 82 may have exemplary resistance values ranging from about 80Ω to about 120Ω, preferably from about 90Ω to about 110Ω, and more preferably from about 95Ω to about 105Ω. Resistor 84 preferably has exemplary resistance values ranging from about 30Ω to about 70Ω, preferably from about 40Ω to about 60Ω, and more preferably from about 45Ω to about 55Ω. Increased values of the resistance of resistor 82 will primarily affect the current that flows through the circuit 70 in reduced power mode and generally decreases the power dissipated by the igniter 52 (and decreases the igniter 52 temperature). Increased resistance values of resistor 84 will generally decrease the igniter 52 temperature in full power mode, and decreased resistance values will increase it.

At the same time, resistor 80 may have exemplary resistance values ranging from about 65Ω to about 95Ω, preferably from about 70Ω to about 90Ω, and more preferably from about 75Ω to about 85Ω. Increased resistance values for resistor 80 will tend to decrease the release voltage (i.e., the resistor 80 input voltage required for the direct current coil 40 to generate a magnetic field sufficient to hold the valve assembly 20 in the open position of FIG. 2) of the direct current coil 40 by allowing more current to flow through the coil 40 a given input voltage to resistor 80. Fuse 88 may be rated, as an example, for about 0.5 A to about 1.5 A, preferably from about 0.6 A to about 1.3 A, and more preferably from about 0.8 A to about 1.2 A. Fuse 78 may be rated, as an example, from about 100 mA to about 300 mA, preferably from about 150 mA to about 250 mA, and more preferably from about 180 mA to about 220 mA.

Example 2

A hold-open circuit 70 as shown in FIG. 5 is provided. Hot surface igniter 52 is as described in Example 1. Zener diode 72 has a breakdown voltage of 5.1 V. Capacitor 74 has a capacitance value of 68 μF. Resistor 80 has a resistance value of 80Ω. Resistor 82 has a resistance value of 100Ω, and resistor 84 has a resistance value of 50Ω. Direct current coil 40 has an inductance of 7.4 μH. The circuit is simulated with a 120 VAC (rms) 60 Hz voltage source signal. FIG. 12A depicts the input voltage at igniter 52 in volts versus time. Circuit 70 is operated in a full power mode in which switch 86 is closed. The input voltage signal seen by the igniter 52 has an rms value of 141.8V, higher than that of the AC source signal owing to the smoothing effect of the capacitors on the ripple produced by diode 64. FIG. 12B shows the current through igniter 52 and has a similar pattern with an rms value of 269 mA. At these voltage and current values, the igniter 52 high temperature resistance would be about 476Ω, and the estimated igniter 52 surface temperature would reach about 2460° F. at steady-state.

FIGS. 12C and 12D show the voltage output from the igniter 52 (i.e., the input voltage at resistor 80) and the current received by direct current coil 40, respectively. As would be expected, the waveforms have a shape similar to those of FIGS. 12A and 12B. However, the igniter 52 output rms voltage is 14.1 V, The rms current to the direct current coil is 100 mA, which is sufficient to latch direct current coil 40 and cooking gas safety valve assembly 20 in the open position of FIG. 2.

FIGS. 13A-13D are simulation results in reduced power mode, i.e., with switch 86 open. As mentioned previously, a reduced power mode is preferably used following ignition and during a cooking operation as a way of preventing flame outs while reducing energy costs and extending the life of igniter 52 relative to operating igniter 52 in a constant full power mode. FIG. 13A shows the igniter 52 input voltage. The wave form is similar to that of FIG. 12A. However, the igniter 52 input rms voltage is 143.2 V. Referring to FIG. 13B, the igniter 52 rms current is 253 mA. At these estimated current and voltage values, the igniter 52 would have a high temperature resistance of about 446Ω and would reach a surface temperature of about 2260° F. at steady state.

FIGS. 13C-13D show the reduced power mode case for the igniter 52 output voltage and the direct current coil 40 current. The average rms current of the direct current coil 40 is about 85 mA, and the igniter 52 output rms voltage value is 30.5V.

Hold open circuits 50 and 70 are particularly suited for situations where the igniter 52 may be energized and remain part of the hold open circuit but receive insufficient current to reach the autoignition temperature of the cooking gas. However, it has been found that with certain igniters 52 that scenario is less likely. In such cases, if the igniter 52 fails to reach the autoignition temperature, the circuit 50 or 70 will have failed as an open circuit. The following hold-open circuits of FIGS. 14 and 15 are particularly well-suited for situations where the igniter 52 is unlikely to fail to reach the autoignition temperature unless it fails as an open circuit. Referring to FIG. 14, a portion of another exemplary cooking gas safety apparatus is depicted which comprises a single mode valve driver hold-open circuit 130. Circuit 130 is powered by a source of alternating current 131. Hold-open circuit 130 converts the alternating-current to a time-varying direct current so that known gas taps with direct current coils like coil 40 may be used. Although not shown, an additional switch would be provided to selectively connect the source of alternating current 131 to the remainder of hold-open circuit 130 when a user actuates the valve assembly 20 by depressing and turning the gas knob stem 26. Hot surface igniter 52 is in electrical communication with direct current coil 40. The term “single mode” refers to the fact that hold-open circuit 130 has a full power mode but no reduced power mode. Thus, igniter 52 can reignite the cooking gas following a flame out by remaining at full power.

Igniter 52 is in series with direct current coil 40. The series combination of igniter 52 and direct current coil 40 is in parallel with capacitor 136. The parallel combination of capacitor 136 and series combination of igniter 52 and direct current coil 40 is in series with diode 132. Diode 132 provides half-wave rectification to the AC signal of AC source 131 so that the voltage seen by igniter 52 at node N₅₂ only has a direct current component. The diode 132 is preferably selected to balance cost and circuit 130 lifetime as diodes with higher current ratings tend to be more expensive while diodes with lower current ratings tend to shorten the lifetime of circuit 130.

Capacitor 136 smooths the ripple in the DC signal provided by diode 132 When diode 132 is forward-biased, capacitor 136 will charge until it reaches is saturation voltage, at which point charging stops. When the diode 132 voltage drops below the saturation voltage of capacitor 136, capacitor 136 will begin to discharge until the AC voltage exceeds the capacitor 136 voltage, at which point it will start charging again. Capacitor 136 has a capacitance value of from about 20 μF to about 40 μF, preferably from about 25 μF to about 35 μF, and more preferably from about 28 μF to about 32 μF. As the capacitance of capacitor 136 increases, the igniter 52 input voltage at node N₅₂ will tend to flatten (show “less ripple”). Conversely, as the capacitance of capacitor 136 decreases, the igniter 52 input voltage at node N₅₂ will tend to be less flat (“more ripple”); The direct current coil 40 has an inductance ranging from about 6 μH to about 9 μH, preferably from about 6.5 μH to about 8.5 μH, and more preferably from about 7.0 μH to about 8.0 μH.

Example 3

A hold-open circuit 130 as shown in FIG. 15 is provided. Hot surface igniter 52 is as described in Example 1. Capacitor 136 has a capacitance of 30 μF. Direct current coil 40 has an inductance of 7.5 μH. The circuit is simulated with a 120 VAC (rms) 60 Hz voltage source signal. FIG. 16A depicts the input voltage at igniter 52 in volts versus time at node N₅₂. The input voltage signal seen by the igniter 52 has an rms value of 118V. FIG. 16B shows the current through igniter 52 and has an rms value of 259 mA. At these voltage and current values, the igniter 52 would have a high temperature resistance of about 457Ω, and the igniter 52 surface temperature would reach about 2340° F. at steady-state

FIGS. 16C and 16D show the voltage output from the igniter 52 and the current received by direct current coil 40, respectively. As would be expected, the waveforms have a shape similar to those of FIGS. 16C and 16D. The rms current to the direct current coil 40 is 259 mA, which is sufficient to latch direct current coil 40 and cooking gas safety valve assembly 20 in the open position of FIG. 2.

Referring to FIG. 15 an exemplary portion of a cooking gas safety apparatus is depicted which comprises a dual mode valve driver hold-open circuit 140. Unlike the hold-open circuit 130 of FIG. 14, the hold-open circuit 140 may be operated in full and reduced power modes. In certain examples, the power provided to igniter 52 in the reduced power mode is from about 70 percent to about 90 percent, preferably from about 75 percent to about 85 percent, and more preferably from about 78 percent to about 82 percent of the power provided to igniter 52 in a full power mode.

Alternating current source 141 supplies alternating current to diode 140 which converts the alternating current to a time-varying direct current. Capacitors 146 and 148 are provided and are in parallel with one another when switch 150 is closed to electrically connect capacitor 148 to the remainder of hold-open circuit 140. Capacitor 146 smooths or flattens the ripple in the input voltage and current to igniter 52 (i.e., at node N₅₂) when hold open circuit 140 is in either the full or reduced power modes. Capacitor 148 smooths or flattens the ripple in the input voltage and current to igniter 52 (i.e., at node N₅₂) when hold open circuit 140 is in the full power mode. When switch 150 is closed, the two parallel capacitors 146 and 148 act as a single capacitor having a capacitance equal to the sum of their respective capacitance values. When switch 150 is open, capacitor 148 is not in the circuit and the total capacitance of the parallel combination of capacitors 146 and 148 equals the capacitance of capacitor 146. In certain exemplary implementations, capacitors 146 and 148 have capacitance values that range from about 10 μF to about 20 μF, preferably from about 12 μF to about 18 μF, and more preferably from about 14 μF to about 16 μF. Direct current coil 40 has the inductance values described previously. When in full power mode, as the capacitance of either or both capacitors 146 and 148 increases, the igniter 52 input voltage and current tend to have less ripple (become flatter), whereas at lower values the converse is true.

Hot surface igniter 52 is in series with direct current coil 40. When switch 150 is open, capacitor 146 forms a parallel combination with the series combination of igniter 52 and direct current coil 40. When switch 150 is closed, the parallel combination of capacitors 146 and 148 forms a parallel combination with the series combination of igniter 52 and direct current coil 40.

When switch 150 is closed, the total capacitance of the parallel combination of capacitors 146 and 148 is higher than the capacitance of capacitor 146 when switch is open. When AC Source 141 is electrically connected to circuit 140 capacitors 146 and 148 will charge until they reach their saturation voltages. When the AC Source signal drops below their saturation voltages, capacitors 146 and 148 will begin to discharge and supply current to igniter 52, thus ensuring that the igniter input voltage at node 52 does not drop below the highest saturation voltage of the capacitors 146 and 148.

Example 4

A hold-open circuit 140 as shown in FIG. 15 is provided. Hot surface igniter 52 is as described in Example 1. Capacitors 146 and 148 each have a capacitance of 15 μF. Direct current coil 40 has an inductance of 7.5 μH. The circuit is simulated with a 120 VAC (rms) 60 Hz voltage source signal. At full power, hold open circuit 140 is equivalent to the hold open circuit 130 of Example 3. Thus, FIG. 16A depicts the input voltage at igniter 52 in volts versus time at full power. The input voltage signal seen by the igniter 52 at node N₅₂ has an rms value of 118 V. FIG. 16B shows the current through igniter 52 and has a similar pattern with an rms value of 259 mA. At these voltage and current values, igniter 52 has a high temperature resistance of about 457Ω, and the estimated igniter surface temperature would reach about 2330° F. at steady-state

As with Example 3, FIGS. 16C and 16D show the voltage output from the igniter 52 and the current received by direct current coil 40, respectively when hold-open circuit 140 is operated in full power mode. As would be expected, the waveforms have a shape similar to those of FIGS. 16C and 16D. The rms current to the direct current coil 40 is 259 mA, which is sufficient to latch direct current coil 40 and cooking gas safety valve assembly 20 in the open position of FIG. 2.

A simulation at 120 VAC source power is carried out with hold-open circuit 140 in reduced power mode, i.e., with switch 150 open using the same igniter 52 and component values as in the full power mode. FIG. 17A depicts the input voltage at igniter 52 in volts versus time at reduced power. The voltage seen by igniter 52 has an rms value of 98 V. FIG. 17B shows the current through igniter 52 in reduced power mode and has a similar pattern with an rms value of 238 mA. At these voltages and currents, the estimated high temperature resistance of igniter 52 is about 414Ω, and igniter 52 would reach an estimated surface temperature of about 2050° F. FIG. 17C shows igniter 52 output voltage. FIG. 17D shows the direct current coil 40 current and has an rms value of 238 mA.

Example 5

Using three igniters 52 each having the same compositions and dimensions which fall within the ranges described in Example 1 but with conductive ink thickness variations on the order of 0.0004-0.002 inches, hold-open circuit 140 is subjected to different AC source voltage signals ranging from 90 VAC rms to 135 VAC rms. The AC power source rms voltage values, igniter input rms voltage values, igniter rms current values, igniter power consumption and measured igniter temperatures are set forth in Tables I-III below:

TABLE I Igniter 1 Igniter Measured Power Igniter Igniter Steady-State Source Igniter current Power Surface VAC VAC mA Consumption Temperature rms rms rms (W) (° F.) 90 84.05 221 18.6 1842 120 116.3 255.6 29.8 2305 135 133.4 274.8 36.6 2528

TABLE II Igniter 2 Igniter Measured Power Igniter Igniter Steady-State Source Igniter current Power Surface VAC VAC mA Consumption Temperature rms rms rms (W) (° F.) 90 81.8 234.1 19.2 1799 120 114 271 31.1 2302 135 131.2 291.3 38.1 2533

TABLE III Igniter 3 Igniter Measured Power Igniter Igniter Steady-State Source Igniter current Power Surface VAC VAC mA Consumption Temperature rms rms rms (W) (° F.) 90 83.8 218.4 18.3 1837 120 117 253.3 29.8 2346 135 133.5 271 36.1 2556

Example 6

A hot surface igniter as described in Example 1 is provided and which has a room temperature resistance of 87Ω. The igniter is placed in hold-open circuit 140 having the component values previously described and subjected to a 120 VAC rms source voltage. The time in seconds required to reach 1800° F. and 2138° F. is provided in Table 4:

TABLE 4 Time (sec) Temperature (° F.) 90 VAC rms 120 VAC rms 136 VAC rms 1800 2.8 0.88 0.7 2138 Not reached 1.9 1.4

Hold-open circuits 50, 70, 130, and 140 are designed to allow the hot surface igniter 52 to be powered by an alternating current source while still being compatible with a direct current coil 40. Because of the relationship between the igniter 52 and the direct current coil 40 in the circuits 50, 70, 130, and 140 the direct current coil 40 only receives sufficient current to hold cooking gas safety valve assembly 20 in the open position of FIG. 2 when the igniter 52 receives enough current to ignite the combustible mixture of air and the cooking gas supplied by valve assembly 20 to the associated burner. However, unlike known hold-open circuits, circuits 50, 70, 130, and 140 do not use a thermocouple to determine when the igniter is hot enough to warrant holding open gas valve 21. In such known systems, the thermocouple introduces a significant amount of lag time because of the dynamics of the thermocouple's response to the ignited flame. Circuits 50, 70, 130, and 140 instead rely on the electrical condition of the igniter 52 to indicate that ignition has occurred or will occur quickly enough to allow gas valve 21 to remain open after the user releases the gas knob. This is possible, at least in part, because of the superior time to ignition temperature properties of the hot surface igniters disclosed herein as suitable for use as igniter 52 relative to known hot surface igniters. Thus, in preferred examples, hot surface igniter 52 is not operatively connected to a thermocouple of a flame sensor.

Referring to FIG. 8, an alternate example of a hold-open circuit 120 is provided in which the hold-open coil 132 operates on alternating current, i.e., it can generate a consistent magnetic field to hold cooking gas safety valve assembly 20 in the open position of FIG. 2 even when the source voltage crosses zero during polarity changes. As known to those skilled in the art, a shading ring may be provided with a standard direct current coil 40 to generate a magnetic field that is secondary to and out of phase with the one generated by the direct current coil 40. As a result, when the primary magnetic field begins to diminish due to the voltage at the hold-open coil 132 approaching zero, the secondary magnetic field generated by the shading ring will hold the valve assembly 20 in the open position of FIG. 2. Referring to FIG. 8, alternating current hold open coil 132 is in series with hot surface igniter 52. Diode 124 is selectively connectable to igniter 52 and alternating current coil 132 to allow hold-open circuit 120 to operate in a reduced power mode, such as during a cooking operation following ignition. As with hold-open circuits 50 and 70, the ability to operate in a reduced power mode reduces the likelihood of a flame-out by providing a constantly energized source of ignition (igniter 52) while reducing power consumption and increasing the igniter life relative to operating the igniter 52 constantly at full power. Switch 130 is selectively connectable to pole 128 to place the hold open circuit in full power mode and to pole 126 to place the igniter 52 in reduced power mode. In certain examples, switch 130 is operatively connected to gas knob stem 26 so that when the gas knob stem 26 is released with the valve assembly 20 in the open position of FIG. 2, the switch 130 connects to pole 126 to operate in the reduced power mode.

As indicated previously, one benefit of using a hot surface igniter 52, as opposed to a spark igniter, to ignite cooktop burner gas is that the igniter can stay continuously energized (at full or reduced power) to provide ignition in the event of a flame-out. This property of hot surface igniters also makes a number of other features possible.

Referring to FIG. 6, a template circuit 90 is depicted which comprises a hot surface igniter 52. FIG. 6 does not show a hold-open circuit or a gas valve with a hold-open coil. However, a gas valve would be provided, and the circuit 90 would be configured such that when the gas valve is actuated, hot surface igniter 52 would be energized via switch 94 to coordinate the flow of gas to the burner with the supply of electricity to the igniter 52. Diode 92 is selectively connectable to the circuit 90 via switch 94. When switch 94 is in contact with switch pole 96, diode 92 is connected to circuit 90 and half-wave rectifies the current supplied to igniter 52. The elimination of the reverse polarity current reduces the power provided to igniter 52, thereby providing a reduced power mode of operation. When switch 94 is in contact with switch pole 98, the circuit 90 is in full power mode. In preferred examples, full power mode is used during an ignition operation, and reduced power mode is used following ignition and during a cooking operation. The template circuit 90 is referred to as such because it includes positions 102 and 104 at which a number of different circuit components may optionally be provided.

Referring to FIG. 6, one component that may be used in positions 102 or 104 is a flame sensor. As is known in the art, flame sensors determine if a burner is lit. A number of different flame sensor technologies exist and may be used, including optical flame detectors and thermocouples. Optical flame sensors may include UV detectors, Near IR array detectors, and IR detectors. If a flame sensor is provided, it may be operatively connected to a gas valve assembly used to supply gas to the burner so that gas flow is discontinued when no flame is present. Flame sensors may also be used with temperature control relays, hold open coils, and bimetallic gas safety valves (“safety cans”) to prevent the flow of burner gas when no flame is present.

A number of sensors or indicators may also be used in positions 102 and 104 to document information about the electrical status of igniter 52. The sensors or indicators may be used alone or in combination with one another. In one example, a timer may be provided which accumulates the total time the igniter 52 is energized. The energization time data may then be used to determine how much of the expected igniter 52 life remains so that the igniter 52 may be replaced before failing. Such collected information may also be transmitted wirelessly by wi-fi, Bluetooth, and other known wireless communication technologies to a user's smart phone, a personal computer, a laptop, or a server to provide information about the status of the igniter 52 remotely.

Audible indicators may also be used in positions 102 and 104. Current spark igniters make a distinct audible sound during ignition, and many consumers have become accustomed to and prefer hearing the sound as an indication of ignition. Hot surface igniter 52 does not make an audible sound during ignition. However, a sound generator may be provided at position 104 which is energized only when igniter 52 is initially energized and which makes a clicking sound or another type of sound to indicate that the igniter 52 is receiving ignition current.

A number of additional sensors and indicators may be used in either position 102 or 104. For example, a fire sensor may be provided. A fire sensor differs from a flame sensor in that it is intended to determine whether a flame other than that desired for cooking is present. The fire sensor is typically an optical sensor with a field of view above the burner. In certain examples, it may be incorporated into a control scheme that shuts of gas to the burner when a fire is detected.

A pot sensor may also be provided. A pot sensor determines when a pot is present on the burner (e.g., by sensing a weight change). The pot sensor may include or be operatively connected to a pressure switch or a plunger that completes circuit 90 only when a pot is present on the burner, which may help prevent fires.

In addition, because igniter 52 may be continuously energized (to full or reduced power) and relit at any gas flow, a number of different cooking functions may be provided by turning the burner on and off (i.e., by opening and closing the gas valve to the burner) for specified periods of time. In certain examples, a timer is provided which accumulates the amount of time the burner is on or off. A flame sensor of the type described previously may be used to toggle the timer state between on and off. Alternatively, the timer may simply be configured to be energized only when the igniter 52 is energized and to accumulate the on and off time when the user sets the gas valve to a certain position that is indicative of a desired cooking mode, e.g., “simmer”. Pre-programmed algorithms present in an associated controller may open and close the burner gas valve based on the selected cooking mode.

The circuit component options described with respect to FIG. 6 may also be used with the direct current hold-open coil circuits described previously. Referring to FIG. 7, hold-open circuit 110 is similar to that of FIG. 4. Direct current coil 40 is part of a gas safety valve assembly 20 of FIGS. 1 and 2. Various sensors and indicators may be used at positions 114 and 116. Hold-open circuit 110 comprises a diode 130 that functions similarly to diode 64 of FIG. 4. Parallel capacitors 120 and 124 smooth the ripple voltage of diode 130 when switch 126 contacts pole 128 (full power mode). Capacitor 120 smooths the ripple voltage in reduced power mode (with switch 126 open). Resistor 122 is in series with direct current coil 40 and limits the current received by direct current coil 40. Shunt resistor 118 shunts the excess current needed to run igniter 52 relative to what is required to hold open the cooking gas safety valve assembly 20 (FIG. 2). 

What is claimed is:
 1. A cooking gas safety apparatus comprising: a valve assembly comprising a valve and at least one coil, the valve comprising a fluid inlet and a fluid outlet and being manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, such that when subjected to a potential difference of 120V AC rms, the hot surface igniter reaches a surface temperature of at least 1400° F. in no more than eight seconds after the at least one coil is subjected to the threshold current.
 2. The cooking gas safety apparatus of claim 1, wherein when subjected to a potential difference of 120V AC rms, the hot surface igniter reaches a surface temperature of at least 1800° F. in no more than four seconds after the at least one coil is subjected to the threshold current.
 3. The cooking gas safety apparatus of claim 1, wherein the at least one coil is at least one alternating current coil.
 4. The cooking gas safety apparatus of claim 1, wherein the at least one coil is at least one direct current coil.
 5. The cooking gas safety apparatus of claim 4, further comprising a diode electrically connectable to the at least one coil and a source of alternating current to supply the at least one direct current coil with a time-varying direct current.
 6. The cooking gas safety apparatus of claim 4, further comprising at least one capacitor, wherein the at least one capacitor is connectable in parallel with the hot surface igniter and the at least one direct current coil.
 7. The cooking gas safety apparatus of claim 1, wherein the at least one coil is not electrically connected to a thermocouple.
 8. The cooking gas safety apparatus of claim 1, wherein the hot surface igniter is a silicon nitride igniter having a room temperature resistance of from about 20 ohms to about 60 ohms.
 9. The cooking gas safety apparatus of claim 1, wherein the ceramic igniter has a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis, the ceramic igniter comprising: first and second ceramic tiles having respective outer surfaces; a conductive ink pattern disposed between the first and second ceramic tiles, wherein the igniter has a thickness along the thickness axis of from about 0.047 to about 0.060 inches and when subjected to a potential difference of 120 V AC rms, at least one of the respective igniter outer surfaces reaches a temperature of at least 1400° F. in no more than 8 seconds.
 10. The cooking gas safety apparatus of claim 9, wherein the conductive ink pattern has a positive temperature coefficient of resistivity.
 11. A cooking gas safety apparatus comprising: a valve assembly comprising a valve and at least one coil, the valve comprising a fluid inlet and a fluid outlet and being manually operable to place the fluid inlet in fluid communication with the fluid outlet, wherein the at least one coil is energizable to hold the valve in the open position only when subjected to a current that exceeds a threshold current value; and and a hot surface igniter electrically connectable to the at least one coil to define a hold-open circuit, such that when subjected to a potential difference of 120V AC rms, a surface of the hot surface igniter reaches an autoignition temperature of at least one of butane, butane 1400, propane, natural gas, and mixtures thereof no more than eight seconds after the at least one coil is subjected to the threshold current.
 12. The cooking gas safety apparatus of claim 11, wherein the surface of the hot surface igniter reaches the autoignition temperature of the at least one of butane, butane 1400, propane, natural gas, and mixtures thereof, no more than four seconds after the at least one coil is subjected to the threshold current.
 13. The cooking gas safety apparatus of claim 11, wherein the at least one coil is at least one alternating current coil.
 14. The cooking gas safety apparatus of claim 11, wherein the at least one coil is at least one direct current coil.
 15. The cooking gas safety apparatus of claim 14, further comprising a diode electrically connectable to the at least one coil and a source of alternating current to supply the at least one direct current coil with a time-varying direct current.
 16. The cooking gas safety apparatus of claim 14, further comprising at least one capacitor, wherein the at least one capacitor is connectable in parallel with the hot surface igniter and the at least one direct current coil.
 17. The cooking gas safety apparatus of claim 1, wherein the at least one coil is not electrically connected to a thermocouple.
 18. The cooking gas safety apparatus of claim 1, wherein the hot surface igniter is a silicon nitride igniter having a room temperature resistance of from about 20 ohms to about 60 ohms.
 19. The cooking gas safety apparatus of claim 1, wherein the ceramic igniter has a ceramic body with a length defining a length axis, a width defining a width axis, and a thickness defining a thickness axis, the ceramic igniter comprising: first and second ceramic tiles having respective outer surfaces; a conductive ink pattern disposed between the first and second ceramic tiles, wherein the igniter has a thickness along the thickness axis of from about 0.047 to about 0.060 inches and when subjected to a potential difference of 120 V AC rms, at least one of the respective igniter outer surfaces reaches a temperature of at least 1400° F. in no more than 8 seconds.
 20. The cooking gas safety apparatus of claim 9, wherein the conductive ink pattern has a positive temperature coefficient of resistivity. 